Move mocks to source packages

With Autoscaler project we've decided to experiment with having mocks created under a dedicated tree (mocks/). This however starts to create more problems than it resolves and having the mocks defined in packages where the interfaces are defined seems to be the best solution.

This MR updates three things:

1. Mocks generation, to create them in-package.
2. The check mocks job to handle the new structure properly.
3. The code coverate report generator, to exclude mocks files from being counted.

It also removes the old mocks/ and internal/mocks/ directories.